The invention is based on a priority application EP 02 360 008.3 which is hereby incorporated by reference. The invention relates to a variable optical delay line and the use of such a variable optical delay line.
Variable optical delay lines are needed to compensate for polarization dispersion (PMD, polarization mode dispersion) and for signal alignment in multiplexers and routers, in particular at high data rates.
Variable mechanical delay lines in which the beam path can be varied by means of mirrors mounted on motors have been disclosed for polarization compensation.
This solution is very slow and very expensive, and severe variations in the delay limit the polarization compensation in higher orders.
Furthermore, cascades of birefringent devices and polarization controllers (PCs) have been disclosed for polarization compensation. EP 0909 045 discloses a variable delay line that can also be constructed in integrated form. The variable delay line comprises a combination of asymmetric Mach-Zehnder interferometers, phase shifters modifying the delay times between the arms of the interferometers. The various individual delays are adjusted by individual controllers of the phase shifters.
Such cascades have many parameters and degrees of freedom that make adjustment difficult and expensive. Furthermore, they have a reduced power.
The object of the invention is therefore to provide a novel variable optical delay line and a use of the novel variable optical delay line.
Said object is achieved by variable optical delay line in accordance with the claims.
The variable optical delay line according to the invention makes possible a steplessly variable delay. The signal is not corrupted during the adjustment of the delay with the phase-shifting elements, which is advantageous for many applications. Any manufacturing inaccuracies are also compensated for by an optoelectrically fed-back drive for the phase controller. The feedback of the phase controller can also be designed for low velocities, which saves costs.
The object is furthermore achieved by a method in accordance with the claims.
The method has the advantage that the desired delay can be adjusted by changing only one parameter.